Thanks for reading Michelle!

To answer your first question, Duncan is not a killer I've studied in great depth yet. So I can't speculate in great detail as to what really motivated him. But watch this space, I'm putting him on the long list of killer's who I'm writing up.

Torture, when being talked about in this context, almost always equals sexual or sexualized torture. When examining this class of criminal, most are motivated by a warped sexual instinct. The instinct can be and is warped in any of a number of ways with serial killers --- that is, anything can be sexualized in a violent way with them. In that way, Freud was correct when he talked about the concepts of eros (the love instinct) and thanatos (the death instinct) getting intertwined and the lines blurred. That's exactly what happens in these cases.

I think it is safe to say Duncan fit that bill but again I can't speak in great detail as to exactly how at this time.